Three different dielectric lens antennas are designed to enhance range of a commercially available 122 GHz radar system-on-chip transceiver with antennas in package. A Fresnel-zoned lens antenna, a plano-hyperbolic lens antenna with one-refracting surface, and a conventional plano-hyperbolic lens antenna with two refracting surfaces are compared. All lens antennas are made of Teflon (PTFE). Problem of back-reflection and its degrading effect on radar performance is addressed. In addition to simulations, an in-house 122 GHz radar system utilizing a system-on-chip transceiver is used to measure radiation pattern, gain, and back-reflection. It is shown that conventional plano-hyperbolic lens antenna with two-refracting surface has higher gain and lower back-reflection than plano-hyperbolic lens antenna with one-refracting surface. However, weak targets near the radar can only be detected by Fresnel-zoned lens antenna which causes no additional back-reflection. If transmit power is increased, Fresnel-zoned lens antenna outperforms conventional plano-hyperbolic lens antenna with two-refracting surfaces.